Blade clamp devices for reciprocating saws are well known in the art. The clamp is used to fix the saw blade to a reciprocating shaft of the saw. The shaft is driven by an electric motor through a gearbox which converts rotary motion of the motor rotor into linear motion. Typically these types of saws comprise a body housing the motor thereby providing means by which the saw can be hand-held. The body of the jigsaw has a longitudinal axis which is generally in-line with the cut direction of the saw blade disposed in the clamp. The motor is generally powered by mains supplied electricity or rechargeable battery.
There are many types of clamping devices available for use on jigsaws. Typically the clamps fall into two categories, namely tool-operated clamps where a tool is required to fix and release the blade to or from the clamp, and tool-free clamps which can be operated by hand. Tool-free clamp devices are generally considered advantageous for jigsaws because the blade can be removed and replaced with relative ease and without the user having to put the tool down and/or find a clamp-release tool.
EP719610A1 and EP792713A2 (which are hereby incorporated in full by reference) both describe tool-free blade clamping devices. Referring to FIGS. 1 and 2, a saw blade clamp comprises a body 3 and a releasable clamping device. The saw blade clamp is shown mounted to a reciprocating shaft 9 of a jigsaw (not shown). The saw blade 11 used for cutting workpieces is held in the clamp 1 by means of the releasable clamping device.
The body 3 has a substantially T-shaped cross section, as shown in FIG. 2. Three sides of a channel 13 are defined in the top of the T, the fourth side of the channel 13 being closed by the reciprocating shaft 9. As can be seen in FIG. 2, the reciprocating shaft 9 includes a V-shaped longitudinal groove 15 which receives an edge of the saw blade 11 to assist in correctly aligning the saw blade 11 for cutting.
The side of the channel 13 opposite to the V-shaped groove 15 is partially open to allow access to the saw blade 11 within the channel 13. Hence, a roller or pin 17 forming part of the releasable clamping device 5 can contact an edge of the saw blade 11. The pin 17 is carried by two torsion springs 19 which are mounted on either side of the channel 13. Each of the torsion springs 19 includes (i) a hooked end 21 engaging a seat 23 forming part of the body 3, (ii) a first helical portion 25 in torsion and (iii) a second helical portion 27 surrounding an end of the pin 17.
The releasable clamping device 5 also includes a substantially U-shaped cross section release device 30. The release device is pivotably connected adjacent ends of the U to opposite surfaces of the body 3, one of which pivots is shown at 32. Each projection on the U comprises an elongate aperture 34 which slidably receives an end of the pin 17. The release device is provided with a colour which is easily distinguishable from the body of the clamping device, so that the device can be readily identified by a user of the jigsaw.
As can be seen in FIG. 1, the pin 17 is arranged to travel in a track 36 formed in the leg of the T-shaped body 3. Hence, if the release device 30, which forms a lever, is pivoted upwards about the pivot 32, the pin 17 is moved away from the saw blade 11, thereby releasing the saw blade 11. Withdrawal of the saw blade 11 can then be affected. Conversely, when the release device is released, the torsion springs 19 urge the pin 17 downwards towards the channel 13 and into contact with the saw blade 11. Clamping or gripping of the saw blade 11 between the pin 17 and the reciprocating shaft 9 is thereby achieved to prevent removal of the saw blade 11 during use of the jigsaw.
As can be seen in FIG. 2, the pin 17 is provided with a circumferential groove 33 which receives the saw blade 11 to assist in aligning the saw blade 11 for cutting. Further, as a result of being cylindrical, the pin can roll along the edge of the saw blade 11 during clamping or release of the saw blade.
However, this type of blade clamp has problems associated therewith; for instance, the pin can move laterally with respect to the reciprocating shaft during use. This lateral movement causes the blade to be misaligned to the longitudinal axis of the jigsaw body, which in turn causes the jigsaw to “crab”.
So-called crabbing occurs when the user has to off-set the alignment of the jigsaw's longitudinal axis with respect to the direction of cut of the blade in order to maintain a straight cut along the intended cut-line. In other words, if the user does not make a compensatory adjustment but maintains the jigsaw's longitudinal axis in alignment with the intended direction of cut, then a misaligned blade (and hence the executed cut in a work piece) wonders from the cut-line. Crabbing is undesirable because the user's perception of the direction in which the jigsaw is cutting can become confused. As a result, the user might have to concentrate on the job in hand, making constant adjustment to the alignment of the jigsaw's body in order to maintain a straight and accurate cut; the cutting action of a crabbing jigsaw can feel unnatural to the user.
FIG. 3 illustrates how misalignment of the blade axis to the blade clamp's body 3, and hence the reciprocating shaft 9, can cause crabbing. FIG. 3 shows only those components of the blade clamp which are relevant for the illustration of crabbing and various components have been omitted for clarity reasons. The pin 17 is held in position by a washer 40, 40′ and circlip 42, 42′. A degree of tolerance is required between the spacing of the circlips and the width of the clamp body in order to maintain fitment of the pin into the clamp track. As a result, the pin does not exactly fit the clamp body and lateral movement of the pin, as indicated by arrow A is possible.
FIG. 3 shows a situation where the pin is clamping a blade 11. The pin has moved to an extreme position within the confines on the circlip and washer arrangement such that the washer 40′on the left hand side is on engagement with the clamp body 3. As a result, the cut direction X of the blade 11 is not longer aligned to the axis Z of the clamp body (and hence the reciprocating shaft) by angle α. Thus, the jigsaw blade will wonder from the cut-line. In order to compensate for this wondering, the operator has to angle the jigsaw body thereby realigning the cut direction with the cut-line.